Effect of hot extrusion on mechanical properties and microstructure of near eutectic Al-12.0%Si-0.2%Mg alloy

Effect of hot extrusion on microstructure and mechanical properties of near eutectic casting Al-12.0%Si-0.2%Mg alloy was investigated by mechanical properties testing and microstructure observation using OM (optical microscope), SEM, and TEM. Dynamical recrystallization of Al matrix, dynamical precipitation of deep sub-micron Si and Mg2Si particles and deformation-induced twinning of Si particle occur during extrusion. The mechanism of dynamical precipitation and recrystallization during hot extrusion for near eutectic Al-Si-Mg alloy is concluded according to microstructure observation. The dynamically precipitated particles are thought to play a Zener pinning role on the growth of recrystallized grains, resultantly leading to a much finer grain size of Al matrix. A good combination of tensile strength (256.3 MPa) and elongation (15.0%) when aged for 12 h after post-extrusion solution treatment is mainly due to fine aging precipitates and recrystallized fine grain structure. The negligible aging hardening effect of extruded samples is due to dynamical precipitation of sub-micron Si and Mg2Si particles.